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><H1
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><A
NAME="CATALOG-PG-ATTRIBUTE"
>45.7. <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
></A
></H1
><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> stores information about
   table columns.  There will be exactly one
   <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> row for every column in every
   table in the database.  (There will also be attribute entries for
   indexes, and indeed all objects that have <TT
CLASS="STRUCTNAME"
>pg_class</TT
>
   entries.)
  </P
><P
>   The term attribute is equivalent to column and is used for
   historical reasons.
  </P
><DIV
CLASS="TABLE"
><A
NAME="AEN85023"
></A
><P
><B
>Table 45-7. <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attrelid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-class.html"
><TT
CLASS="STRUCTNAME"
>pg_class</TT
></A
>.oid</TT
></TD
><TD
>The table this column belongs to</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attname</TT
></TD
><TD
><TT
CLASS="TYPE"
>name</TT
></TD
><TD
>&nbsp;</TD
><TD
>The column name</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>atttypid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-type.html"
><TT
CLASS="STRUCTNAME"
>pg_type</TT
></A
>.oid</TT
></TD
><TD
>The data type of this column</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attstattarget</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>       <TT
CLASS="STRUCTFIELD"
>attstattarget</TT
> controls the level of detail
       of statistics accumulated for this column by
       <A
HREF="sql-analyze.html"
>ANALYZE</A
>.
       A zero value indicates that no statistics should be collected.
       A negative value says to use the system default statistics target.
       The exact meaning of positive values is data type-dependent.
       For scalar data types, <TT
CLASS="STRUCTFIELD"
>attstattarget</TT
>
       is both the target number of <SPAN
CLASS="QUOTE"
>"most common values"</SPAN
>
       to collect, and the target number of histogram bins to create.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attlen</TT
></TD
><TD
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
>&nbsp;</TD
><TD
>       A copy of <TT
CLASS="LITERAL"
>pg_type.typlen</TT
> of this column's
       type
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attnum</TT
></TD
><TD
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
>&nbsp;</TD
><TD
>       The number of the column.  Ordinary columns are numbered from 1
       up.  System columns, such as <TT
CLASS="STRUCTFIELD"
>oid</TT
>,
       have (arbitrary) negative numbers.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attndims</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Number of dimensions, if the column is an array type; otherwise 0.
       (Presently, the number of dimensions of an array is not enforced,
       so any nonzero value effectively means <SPAN
CLASS="QUOTE"
>"it's an array"</SPAN
>.)
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attcacheoff</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Always -1 in storage, but when loaded into a row descriptor
       in memory this might be updated to cache the offset of the attribute
       within the row
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>atttypmod</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>       <TT
CLASS="STRUCTFIELD"
>atttypmod</TT
> records type-specific data
       supplied at table creation time (for example, the maximum
       length of a <TT
CLASS="TYPE"
>varchar</TT
> column).  It is passed to
       type-specific input functions and length coercion functions.
       The value will generally be -1 for types that do not need <TT
CLASS="STRUCTFIELD"
>atttypmod</TT
>.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attbyval</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>       A copy of <TT
CLASS="LITERAL"
>pg_type.typbyval</TT
> of this column's type
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attstorage</TT
></TD
><TD
><TT
CLASS="TYPE"
>char</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Normally a copy of <TT
CLASS="LITERAL"
>pg_type.typstorage</TT
> of this
       column's type.  For TOAST-able data types, this can be altered
       after column creation to control storage policy.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attalign</TT
></TD
><TD
><TT
CLASS="TYPE"
>char</TT
></TD
><TD
>&nbsp;</TD
><TD
>       A copy of <TT
CLASS="LITERAL"
>pg_type.typalign</TT
> of this column's type
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attnotnull</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>       This represents a not-null constraint.  It is possible to
       change this column to enable or disable the constraint.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>atthasdef</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>       This column has a default value, in which case there will be a
       corresponding entry in the <TT
CLASS="STRUCTNAME"
>pg_attrdef</TT
>
       catalog that actually defines the value.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attisdropped</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>       This column has been dropped and is no longer valid.  A dropped
       column is still physically present in the table, but is
       ignored by the parser and so cannot be accessed via SQL.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attislocal</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>       This column is defined locally in the relation.  Note that a column can
       be locally defined and inherited simultaneously.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attinhcount</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>       The number of direct ancestors this column has.  A column with a
       nonzero number of ancestors cannot be dropped nor renamed.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attcollation</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-collation.html"
><TT
CLASS="STRUCTNAME"
>pg_collation</TT
></A
>.oid</TT
></TD
><TD
>       The defined collation of the column, or zero if the column is
       not of a collatable data type.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attacl</TT
></TD
><TD
><TT
CLASS="TYPE"
>aclitem[]</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Column-level access privileges, if any have been granted specifically
       on this column
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>attoptions</TT
></TD
><TD
><TT
CLASS="TYPE"
>text[]</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Attribute-level options, as <SPAN
CLASS="QUOTE"
>"keyword=value"</SPAN
> strings
      </TD
></TR
></TBODY
></TABLE
></DIV
><P
>   In a dropped column's <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> entry,
   <TT
CLASS="STRUCTFIELD"
>atttypid</TT
> is reset to zero, but
   <TT
CLASS="STRUCTFIELD"
>attlen</TT
> and the other fields copied from
   <TT
CLASS="STRUCTNAME"
>pg_type</TT
> are still valid.  This arrangement is needed
   to cope with the situation where the dropped column's data type was
   later dropped, and so there is no <TT
CLASS="STRUCTNAME"
>pg_type</TT
> row anymore.
   <TT
CLASS="STRUCTFIELD"
>attlen</TT
> and the other fields can be used
   to interpret the contents of a row of the table.
  </P
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